The invention relates to an infinitely variable traction roller transmission in which power is transmitted through traction rollers which are pivotally supported between toric input and output discs with which they are forced into firm engagement for the transmission of motion therebetween.
In such transmissions, the traction rollers are mounted on support structures which, when pivoted, cause engagement of the traction rollers with the toric discs in circles of varying diameters depending on the desired transmission ratio. The support structures are generally trunnions which are supported in a housing in such a manner that they are either axially movable or slightly tiltable for initiating a change in the transmission ratio, To provide for slight axial movability, for example, two traction roller support trunnions may be supported opposite one another by flexible tension sheets as shown in U.S. Pat. No. 4,086,820 which issued May 2, 1978 to Charles E. Kraus, To provide for slight tilting, traction roller support trunnions may be supported by a roller rolling along a partial circular track wherein one end of the trunnion is movable for tilting the trunnion in order to initiate a change in transmission ratio as disclosed in U.S. Pat. No. 4,964,312 which issued Oct. 23, 1990 to Charles E. Kraus.
For the transmission of large torques the forces with which the traction rollers have to be engaged with the toric discs are rather large. They may be provided either by forcing the toric discs toward one another or by forcing the traction roller axially into the toric cavity formed between the toric discs. This may be accomplished hydraulically by an arrangement as shown, for example, in U.S. Pat. No. 4,576,055 which issued Mar. 18, 1986 to Charles E. Kraus.
It is desirable to produce the contact forces directly under the traction roller in axial direction of the traction roller such that the required fluid traction coefficient will remain relatively constant over the selected transmission ratio range. Then a relatively large ratio range can be accommodated without overloading the contact areas in the pivotal end positions of the trunnions.
However since the required contact forces are very large and the space under a traction roller is quite limited, a large hydraulic fluid pressure is required to produce the needed contact forces. The large fluid pressures require high pressure pumps and high pressure seals which are expensive and more easily subject to failure than lower pressure components.
It is therefore the principal object of the present invention to provide an infinitely variable traction roller transmission and particularly a traction roller support arrangement which generates the large contact forces needed for the engagement of the traction rollers with the toric discs with a hydraulic operating fluid of only relatively low pressure and which is therefore reliable in operation and relatively inexpensive to manufacture.